Multilayer article having a planarized outer layer comprising a toughened polycyanurate

ABSTRACT

An electronic circuit package comprising an electrically conductive circuit layer on a polymer, ceramic or multi-layer substrate wherein a curable dielectric material is applied over the electrically conductive circuit layer. The curable dielectric material comprises a blend of a fluorine-containing cyanate and a fluorine-containing arylene ether polymer. The cyanate is a monomer having the structure 
     
         N.tbd.C--O--R--[R.sup.1 ].sub.n --O--C.tbd.N 
    
     and the fluorine containing arylene ether polymer has the structure 
     
         X--R--[R.sup.1 ].sub.m --X 
    
     wherein X is any group capable of reacting with a --C.tbd.N group; 
     R is an aliphatic or aromatic group which may or may not be fluorosubstituted; 
     R 1  is an aliphatic or aromatic group which may or may not be fluoro substituted or R 1  is selected from the group consisting of ether, carbonyl, sulfone, phosphine oxide and sulfide, and at least one of R or R 1  must be fluoro substituted; 
     n is 0-10; and 
     m is 0-100. 
     The dielectric material in the cured state comprises a fluorine-containing polycyanurate network having a plurality of discrete phases of the fluorine-containing thermoplastic polymer dispersed therein. The thermoplastic polymer phases are of submicron size.

This application is a Division of Ser. No. 07/923,723, filed Jul. 31,1992, pending.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The present invention relates generally to a curable cyanate resincomposition having enhanced fracture resistance as a result of theincorporation of reactive thermoplastic oligomers therein. Morespecifically, the present invention relates to a composition comprisingdicyanate ester resins containing at least one thermoplastic polymermodifier which is soluble in the dicyanate ester resin. Saidthermoplastic polymer undergoes an in-situ phase separation processduring cure to form a microphase-separated multiphase thermosetmaterial.

Accordingly, the present invention embodies low dielectric constantmaterials with adjustable properties such as glass transitiontemperature and fracture toughness. The modified cyanate resin has a lowdielectric constant and when impregnated into various types ofreinforcements, yields insulating materials with either a controlledcoefficient of thermal expansion (CTE) or a very low dielectric constantor both.

Furthermore, this invention relates to a curable material useful inconducting heat or electricity comprising a modified cyanate resinmaterial and inorganic or metal particles which exhibits high thermalstability, adjustable glass transition temperature with controlled CTE.

Furthermore, the present invention relates to a curable material usefulin the fabrication of prepreg layers for use in the manufacture ofelectronic packaging structures, adhesives and aerospace structuralarticles.

Furthermore, this invention relates to a material for use in electronicpackaging applications where a thermoset material is required which haslow dielectric constant and adjustable properties such as glasstransition temperature and fracture toughness, and a process for makingthe material.

More particularly, this invention relates to a modified cyanate resinmaterial useful in the fabrication of printed circuit boards,semiconductor chip carriers, metal-core boards, reaction injectionmolded (RIM) cards, multichip modules, and multilayer thin film circuitstructures, which may include more than one conductive layer and mayincorporate electrical interconnections including through-holes or viasbetween two or more conductive layers or blind vias between two layers.This invention is well suited for use as a substrate material forsurface mounted electronic components.

In addition, this invention relates to an improved material and printedcircuit board made therefrom comprising a modified cyanate resinmaterial and reinforcement which exhibits high thermal stability,adjustable glass transition temperature, flame retardancy with either acontrolled CTE, or low dielectric constant or both.

PRIOR ART

Polycyanurate thermosets based upon certain cyanate ester resins possessa number of attractive properties such as low dielectric constant,excellent thermal stability, low moisture uptake, high glass transitiontemperature, and processability characteristics analogous to epoxyresins (melt or solution processable).

Other attractive properties of these polycyanurate thermosets include,methyl ethyl ketone solubility, no volatile formation upon curing,outstanding adhesive properties, photoimageability (if desired) andinherent flame retardancy.

However, use of these polycyanurate thermoset materials in electronicpackaging applications (e.g., prepregs, laminates, circuit boards) islimited due to their brittle nature which makes them susceptible tocracking when stressed or during processing such as via formation. Thisinherent brittleness is due to the high crosslink density of thenetworks which results in poor fracture toughness. Although there havebeen significant efforts to enhance the fracture toughness of theaforementioned polycyanurates, further improvement in the mechanicalproperties of these materials is required in order to make them usefulin packaging. (As used herein, "fracture toughness" is a measure of howmuch energy is needed to propagate a crack in the plastic.)

U.S. Pat. No. 4,147,360 to Prevorsek et al., discloses a compositioncontaining a crosslinked polycyanurate network in which a high molecularweight polyester carbonate, is finely dispersed.

This reference is similar to the present invention in that athermoplastic is chemically incorporated into a polycyanurate thermosetto enhance the physical properties.

In Prevorsek et al., the chemical structures of both the cyanate esterresins and the thermoplastic modifier are different from those disclosedin the present invention. The present invention discloses highlyfluorinated materials that possess high T_(g) 's, low dielectricconstants, inherent flame retardancy, and methyl ethyl ketonesolubility.

Prevorsek et al. describe the use of solvent "to cause simultaneousprecipitation of the thermoplastic polymer and dicyanate monomer."

Contrary to Prevorsek et al., the present invention describes for thefirst time, a fluorine-containing thermoplastic polymer (i.e., amodifier) which actually dissolves in the dicyanate monomer resin. Soessentially, the dicyanate is a solvent for the modifier polymer. Thisphenomenon is the key to obtaining microphase separation during thermalcuring of the composition of the present invention and hence theresulting improved mechanical properties. This is different from theapproach utilized by Prevorsek et al. where what phase separation thatdoes occur, occurs during solvent evaporation, well before the thermalcure. This is an important distinguishing feature that allows for thevery small phases present in the present invention.

U.S. Pat. No. 4,902,752 to Shimp discloses toughening polycyanurateswith thermoplastics. Shimp discloses other relevant prior art referencestherein, the contents of which are hereby incorporated by referenceherein. More particularly, Shimp discloses curable compositions madefrom blends of polycyanate esters of polyhydric phenols in admixturewith amorphous, aromatic thermoplastic resins which are initiallysoluble in the polycyanate ester but which phase separate during curing.The reactant materials of Shimp will not function according to thepresent invention because they are difficult to process and the solventsused inherently raise environmental concerns. In the present inventionthe chemical structures of both the cyanate ester resin and thethermoplastic are different from those disclosed by Shimp et al.

European Patent Application 0 412 827 A2 to Mackenzie et al., disclosesa fiber reinforced resin composition containing a polyarylsulfonethermoplastic compound and a cyanate ester resin. This reference issimilar to the present invention in that a thermoplastic is chemicallyincorporated into a polycyanurate thermoset to alter the physicalproperties. One difference between the present invention and thereference is that the chemical structures of both the cyanate esterresins and the thermoplastic modifier are different. The presentinvention embodies highly fluorinated materials that possess high T_(g)'s, low dielectric constants, inherent flame retardancy, and methylethyl ketone processability. The resin composition described byMackenzie et al. is not methyl ethyl ketone soluble, does not possessflame retardant properties and does not possess an inherently lowdielectric constant. These attributes are unique to the presentinvention and are essential for electronics applications where solutionprocessing is utilized.

U.S. Pat. No. 4,745,215 to Cox et al. discloses that dicyanate diphenylhexafluorinated alkanes can be impregnated into suitable reinforcingfabrics and heat cured at elevated temperatures above their glasstransition temperatures, i.e., about 320° C. for 1 hour. The curedproducts have favorable properties for high temperature and/orelectrical insulation uses, such as in laminated circuit boards. Theseproperties include low dielectric constants, high glass transitiontemperatures and high thermal degradation temperatures. However, it isalso recognized that such systems have low fracture resistance andtherefore need to be improved for use in electronic packaging.

SUMMARY OF THE INVENTION

The present invention comprises a novel modified polycyanurate resinpossessing enhanced fracture toughness and improved drillability. Themodifiers suitable for use are tough, ductile engineering thermoplasticspossessing relatively high glass transition temperatures (T_(g)) (i.e.,between about 140° and 200° C.) which when combined with thepolycyanurate network do not reduce high temperature stability. Thematerials have a high T_(g), low dielectric constant and can beprocessed with conventional techniques.

The present invention improves the fracture toughness of thermosettingpolymers based on the cyanate ester chemistry. It involves theincorporation of specifically tailored thermoplastic polymers into athermoset network. These modifiers have an inherent low dielectricconstant, and coupled with the use of fluorinated dicyanates, yieldsthermoplastic modified (TPM) polycyanurate material with a lowdielectric constant. The polymer blend composition has significantlyenhanced fracture thoughness and high resistance to thermal degradation.

Polymeric materials used for printed circuit boards require fracturethoughness, i.e. the ability to avoid surface cracks resulting fromhandling and use. Currently used materials such as epoxy resins (FR4)have a fracture toughness in the range of 70-90 J/m². Untoughenedpolycyanurates have a fracture toughness in the range of 50-70 J/m². Themodified polycyanurates of the present invention, on the other hand,have a toughness as high as 100-680 J/m².

The polycyanurate of the present invention is fluorinated having lowdielectric constant. The monomer precursor to the fluorinatedpolycyanurate is a dicyanate compound or prepolymer thereof or both,alone or in combination referred to herein as a "resin." The dicyanateresin is mixed with a thermoplastic polymer. The thermoplastic has beentailored to be soluble in the fluorinated dicyanate resin. Thethermoplastic is synthesized to contain similar chemical substituents tothose on the polycyanurate. This similarity retards phase separation ofthe polycyanurate and the thermoplastic. When the mixture is heated, themonomer begins to crosslink. As the molecular weight of the polymerizingmonomers increases, the thermoplastic additive becomes slightly lesscompatible with the polymerized monomers and begins to phase separate.When the crosslinking reaction is complete, the final compositioncontains a fluorinated polycyanurate with thermoplastic phases on thesubmicron scale which it is believed, results in the substantialincrease in fracture toughness. If a prepolymer is used, the reactionproceeds in the same manner. Optionally, by blending different cyanatemonomers such as one having low T_(g), and one having high T_(g) anintermediate T_(g) material is formed which maintains the physicalproperties of the high T_(g) material, such as the desired fracturetoughness.

Cyanate ester resins are bisphenol derivatives containing thering-forming cyanate (--C.tbd.N) functional group. This family ofthermosetting monomers and their prepolymers are esters of bisphenolsand cyanic acid which cyclotrimerize to form substituted triazine ringsupon heating. Conversion, or curing, to high T_(g) thermoset materialforms three-dimensional networks of oxygen-linked triazine rings andbisphenol units, correctly termed polycyanurates. The cyclotrimerizationreaction is classified as addition polymerization. A schematic of thecrosslinking mechanism is shown in FIG. 1.

The cyanate structures embodied within the scope of the presentinvention are:

    N.tbd.C--O--R----R'].sub.n --O--C.tbd.N

wherein R is an aliphatic or aromatic group which may or may not befluorosubstituted;

R' is an aliphatic or aromatic group which may or may not befluorosubstituted, or it can be ether, carbonyl, sulfone, phosphineoxide, sulfide, or nothing, and at least one of R or R' must befluorosubstituted, and

n is 0-10

The cyanate that can be used pursuant to the present invention alsocomprises prepolymers of said monomers or blends thereof.

Some suitable fluorinated cyanate structures that fall within the scopeof the invention are: ##STR1##

The thermoplastic modifiers used as modifiers in accordance with thepresent invention are:

    X--R----R'].sub.n --X

wherein X is any group capable of reacting with a --CN group, such ashydroxyl, amino, cyanato, epoxy; and

wherein R is a aliphatic or aromatic group which may or may not befluorosubstituted;

R' is an aliphatic or aromatic group which may or may not befluorosubstituted or it can be ether, carbonyl, sulfone, phosphineoxide, sulfide, or nothing, and at least one of R or R' must befluorosubstituted, and

n is 0-100.

Specific examples of suitable thermoplastic modifiers that can be usedin the present invention are: ##STR2##

As depicted above, suitable modifiers include any fluorine containingpoly(arylene ether), or other thermoplastic which is compatible with thecyanate ester resin comprising monomer, prepolymer or blend thereof.

As noted above, in the reaction used to form the network, the cyanatemonomer initially acts as a solvent for the thermoplastic modifier.

The reaction begins first by branching and chain extension within thecyanate monomer and between cyanate groups and endgroups ofthermoplastic resin.

As the cyanate resin becomes highly branched and crosslinked,thermoplastic polymer chains start forming domains as driven bythermodynamic principles and the reaction proceeds substantially tocompletion.

At the end of the reaction, these domains have grown into phases ofmicroscopic sizes (angstroms to microns) rich in thermoplasticsurrounded by a highly crosslinked matrix of polycyanurate network.

Useful features which have been designed into the aforementioned systeminclude:

1. A thermoplastic polymer is used which is initially soluble indicyanate ester resin at a temperature of approximately 20° C. above themelting point of the resin (100°-110° C.). This thermoplastic undergoesan in-situ phase separation process during network formation to form amicrophase separated multiphase network. To achieve these criteria thebackbone structure of the thermoplastic modifier is selected anddesigned with the intent of maximizing compatibility. Of the manysystems tested, only the fluorine based modifiers were found to have therequired miscibility with the dicyanate resin which is a prerequisitefor achieving the subsequent network properties.

2. Methyl ethyl ketone solubility of the thermoplastic makes this asystem which is compatible with today's industrial environmentalrequirements. This is essential so that this material can be processedwith the existing technologies currently utilized in the fabrication ofprinted circuit boards. Typically, high T_(g) thermoplastics of thistype are only soluble in polar aprotic solvents or chlorinated solventswhich are not environmentally acceptable.

3. The introduction of reactive functional groups (i.e., hydroxyl, aminoor cyanato) on the terminal ends of the thermoplastic modifier isespecially beneficial. This allows the thermoplastic to be chemicallyincorporated (covalently bonded) into the network structure. Chemicalincorporation enhances the compatibility of the modifier and results ina more uniform morphology. It also insures that solvent resistance inthe cured network is maintained.

4. Molecular weight control of the thermoplastic modifier is provided.The solubility, morphology, modulus, and fracture toughness of themodified polycyanurates are a function of the molecular weight of thethermoplastic modifier. Typically, the optimum molecular weight is inthe range of 13,000 to 18,000 g/mol. This molecular weight range is justabove the critical molecular weight for entanglements of these polymers.If melt processability is desired, lower molecular weights (5,000 to13,000 g/mol) may be required to reduce the melt viscosity.

5. Optimal composition of the thermoplastic modifier in the fluorinateddicyanurate resin ranges between 5 to 40 weight/weight percent. Theresulting properties such as fracture toughness, morphology, modulus,dielectric constant, etc. are all a function of chemical nature of themodifier which has been designed in this case to provide improvedmechanical performance without sacrificing the desirable properties ofthe polycyanurate thermoset material.

6. The backbone structures of the thermoplastic modifiers are tailoredto reduce their dielectric constants. This is achieved by theincorporation of fluorine containing moieties in the backbone of thepolymer.

Another aspect of the present invention is the modification of theproperties of the polycyanurate resins disclosed herein and morespecifically, to provide thermosetting resins resulting from thecyclotrimerization of 4,4'-(hexafluorobisphenol AF dicyanate)(6F-Dicyanate) with a lower Tg high performance dicyanate e.g.4,4'-(1,3-phenylenediisopropylidene) diphenylcyanate (M-Dicyanate) and athermoplastic based upon bisphenol AF poly(arylene ether sulfone) orpoly(arylene ether ketone). This produces cured laminates having reducedcure temperatures and improved fracture toughness compared to the6F-Dicyanate based networks. The resulting resins display hightemperature resistance, low dielectric constants and most importantly,flame resistance. Some additional non-fluorinated cyanate structuresthat fall within the scope of the invention are: ##STR3##

In addition, the properties (i.e., mechanical dielectric, thermal,adhesive, morphological and flame retardant) may be modified by blendingwith other thermosetting resins such as epoxy, bismaleimide,benzocyclobutene, bisnadimide and diacetylene resins. An illustrativepartial list of suitable thermosetting resins that fall within the scopeof the invention are: ##STR4##

A further embodiment of this invention is a polycyanurate materialhaving enhanced fracture toughness to permit the fabrication ofcomposites having high percentage loading of metal or inorganicparticles. Incorporation of metal, inorganic particles, pigments orfillers often have a deleterious effect on the mechanical properties ofa composite which generally comprises a thermoset binder. The fillersact as sites where stress is concentrated and increase the modulus whichin turn decreases the fracture toughness. The use of a modified cyanateresin overcomes this deficiency.

Composite materials comprising the modified polycyanurate and conductingmetal particles, pigments or fillers are useful in fabricatingconductive articles and/or adhesives. Examples of conductive metalsuseful in the present invention are copper, nickel, gold, platinum,palladium, zinc and others or alloys or mixture thereof. Such compositesare useful in making electrical contacts or interconnections inelectronic device application, or for shielding and electrostaticdischarge uses. Electrically conductive adhesives are another possibleuse for electrically conductive modified polycyanurates. Higherconductivities are possible with the system since they allow greaterloading without sacrificing mechanical properties.

Composite materials comprising the modified and thermally conductiveparticles pigments, or fillers are useful in fabricating heat conductivearticles and/or adhesives. Examples of thermally conductive fillersinclude boron nitride, zinc, oxide, aluminum nitride and diamond.

Heat conductive composite materials are used for thermal management ofelectronic packaging, power supply systems, chip attachment, and heatsink attachment. Heat conductive materials are needed for removingresistive thermal energy or distributing the heat over a larger surfacearea to facilitate its transfer into the environment through airconvection, or by contact with a liquid or a solid.

Future high performance or high density circuit packaging will operateat higher temperature due to the increased density of integratedcircuits and greater power which necessitates the use of enhanced heatconductive materials having improved glass transition temperatures andfracture toughness as provided by the modified polycyanurate material.

The thermoplastic modified polycyanurates of this invention have beenshown to have far higher temperature stability (up to 300° C.) thanepoxy resins. The adhesion to of polycyanurates to metals, notably tocopper, is in the range of 8-11 lbs/inch. In addition, the dielectricconstants of the modified (toughened) polycyanurates are much lower(2.6-2.8) than for epoxy resins (3.5-4.0). Furthermore, the improvedfracture toughness of the modified polycyanurates permit higher loadingof the conductive pigments to provide greater heat conductivity withoutsacrificing mechanical integrity.

It has been determined that hollow glass spheres or silica spherefillers can be used to reduce the dielectric constant of glassreinforced composites. For example, the hollow glass spheres or silicaspheres can be usefully blended into the prepreg in the range of betweenabout 25 and 65 volume percent, each of the spheres having a diameter inthe range of between about 5μ and 25μ. A more complete discussion of theeffect of the incorporation of these spheres into the prepreg and withrespect to the reduction of dielectric constant is found in IBMdisclosure EN 989,020 the contents of which are hereby incorporated byreference herein.

With the increased use of surface mount and direct chip attachtechnologies, there is a need to have a dielectric material possessing alow coefficient of thermal expansion (CTE). Typical epoxy/glass clothcomposites have CTE's in the range of 15-30 ppm/°C. depending on theresin content. Silicon has a CTE in the range of 3-5 ppm/°C.

It has been determined that the composition of the present inventionimpregnated into a reinforcing matrix of glass fabric, a woven ornonwoven mat made of a material such as an aramid fiber or a metal filmsuch as a copper/Invar/copper composite can successfully reduce thein-plane CTE.

One embodiment of the present invention is the use of the blendcomposition to form glass cloth reinforced dielectrics. For many years,glass cloth has been used to reduce the in-plane CTE in epoxy/glasscloth composites. The glass acts as a constraining layer, thus reducingthe CTE of the ply. The most common glass cloth is E-glass. The drawbackof E-glass has been its high dielectric constant. By using glass cloth,the dielectric constant of the ply is increased. Therefore, there is aneed to use a combination of a low dielectric constant thermosettingresin and a lower dielectric constant woven-glass cloth.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic formula representation showing the crosslinkingmechanism that occurs during reaction.

FIG. 2 is a schematic of a continous lamination process.

FIG. 3 is a plot of dynamic mechanical behavior of the composition ofthe present invention.

FIG. 4 is a plot showing the effect of thermoplastic modifierconcentration on fracture toughness of the blends of the presentinvention.

FIG. 5 is a plot of the effect of the cyanate blend composition on thefracture toughness of the blends of the present invention.

FIG. 6 is a plot of the effect of varying one of the cyanates in acyanate blend on the thermoset T_(g).

FIG. 7 is a plot of the effect of cyanate blends on the fracturetoughness of the modified polycyanurates of the present invention.

DESCRIPTION OF THE INVENTION PREFERRED EMBODIMENTS

While the present invention relates to dicyanate ester resins,preferably the invention relates to hexafluoroisopropylidene dicyanateester resins containing a thermoplastic polymer which is soluble in thedicyanate ester resin. This thermoplastic polymer undergoes an in-situphase separation process during network formation to form amicrophase-separated multiphase thermoset material. Reactive functionalgroups such as a hydroxyl group modifier permit the modifier to beincorporated by covalent bonding into the polymer network structure.Using monomers containing fluorine groups provides a lower dielectricconstant. Examples of such thermoplastic modifiers include (a)poly(arylene ether sulfone) prepared by reacting bisphenol AF with4,4'-difluorodiphenylsulfone; and (b) a poly(arylene ether ketone) madeby reacting bisphenol AF with 4,4'-difluorobenzophenone. Thermoplasticmodified polycyanurates are prepared by reacting M-dicyanate and6F-dicyanate with the thermoplastic modifier in two stages. In the firststage, the thermoplastic modifier and dicyanate ester resins aremechanically mixed under vacuum at 130° C. to form a transparenthomogeneous mixture. In the second stage the reactants were cured atabout 200° to 250° C. for one hour and at about 250° C. to 325 ° C. fortwo hours.

The polycyanurate networks in this case are based upon the reaction ofM-dicyanate and 6F-dicyanate with a thermoplastic modifier shown below:##STR5##

Both of the specific preferred sulfone and ketone thermoplasticmodifiers noted above are successfully incorporated into networks in arange of 5 to 40 wt/wt percent preferably between 15 and 30 wt/wtpercent.

The thermoplastic modifiers used in the present invention can beconveniently synthesized via nucleophilic aromatic substitutionreactions. A poly(arylene ether sulfone) is synthesized by reactingbisphenol AF with 4,4'-difluorodiphenylsulfone. Likewise, thepoly(arylene ether ketone) is synthesized by reacting bisphenol AF with4,4'-difluorobenzophenone. In the course of the reaction, molecularweight and endgroup functionality are controlled by offsetting thestoichiometry in the reaction according to the Carrothers equation. Anexcess of the bisphenol AF reactant is utilized to achieve hydroxylendgroups and an approximate number average molecular weight of 15,000g/mol for both polymers.

A common way of reducing in-plane CTE of cured laminates is to solutionimpregnate or melt impregnate the cyanate resin into a woven glasscloth. The choice of the specific glass cloth will dictate thedielectric constant of the resulting composite structure. E-glass is themost commonly utilized cloth fabric, however, it has a dielectricconstant of about 5.8. The resulting composite with cured polycyanuratewill be in the range of 3.4 to 3.5.

Other glass cloths such as S-glass, D-glass, K-glass or Q-glass possesslower dielectric constants in the range of 3.2-3.4 and result in a curedlaminate possessing a dielectric constant in the range of about 3.0-3.2.

The invention described here also involves solvent impregnation of asolution of the thermoplastic modified fluorinated cyanate blend intoaramid fibers. Both DuPont (tradename Thermount) and Teijin Ltd(tradename Technora) have developed chopped aramid fiber mats. A typicalaramid fiber mat, suitable for use in the present invention is the matmade from co-poly-phenylene 3,4'oxydiphenylene terephthalamide referredto as "PPODTA." The in-plane CTE of a mat such as a PPODTA mat (withoutresin) is on the order of -6 to -7 ppm/°C. (10⁻⁶ in/in/°C.). At a resincontent of 50-60%, the in-plane CTE is in the range of 3-8 ppm/°C. Thisis very closely matched with the CTE of silicon and would not requirethe use of encapsulants to stabilize the chip during thermal cycling. Toillustrate the benefits of the invention, the Er of the PPODTA paper is3.5. At 60 percent resin content the dielectric constant is about 2.8 to3.0.

Another strategy for lowering the in-plane CTE of a composite is to usecopper/Invar/copper as the constraining layer and also to serve as apower core. There are two approaches to fabricating this type of core.The first involves laminating a reinforced dielectric sheet, such as theS-glass, D-glass, or Q-glass dielectrics. The added benefit here is thatthe overall in-plane CTEs of both the Cu/Invar/Cu and the dielectric plyare low. Dielectric plies fabricated using the modified cyanate resinsimpregnated into the DuPont Thermount or Teijin Technora mat can also beutilized to fabricate a controlled CTE encapsulated power corestructure.

An alternate method is to coat the Cu/Invar/Cu core using a continuouslamination process as depicted in FIG. 2. The advantage of this methodis that it is continuous and uses no solvents. Due to the uniquecompatibility of the thermoplastic modifier in the cyanate resins, theCu/Invar/Cu core can be coated using a melt process. A layer of meltedresin 1 is applied to the continuously moving upper surfaces of webs ofCu strip 2 and upper Cu strip 3 of the core using a doctor blade or slitextrusion heads 5, 6. A web of Cu foil 4 is secured to resin layer 1atop strip 3 at pressure rolls 7 and 8 and then between heated platens 9(now shown) under pressure. The temperature of the platens 9 ismaintained in the range of 180°-325° C. In the double belt laminationportion of the lamination process, pressure is applied initally at rolls7 and 8 and the temperature of platens 9 is rapidly increased throughthe range noted above, consolidating the resin and causing thecrosslinking reaction to occur. The curing temperature is dependent onthe composition of the cyanate blend ratio of M-Dicyanate to6F-Dicyanate. The resulting product is wound on roll 10.

Copper clad cores may be fabricated by placing multiple plies of prepregbetween oxide treated copper foils and laminating under heat andpressure. Typically, the lamination process involves heating the copperfoil and prepreg stack at between 5° to 10° C./min to the final platensetpoint. The platen setpoint is determined by the final T_(g) of thematrix resin. The ensure full cure during the lamination process, thefinal temperature is set to be approximately 25° C. above the T_(g) ofthe fully cured matrix. The pressure is typically in the range of200-500 pounds per square inch, with the preferred pressure being 300pounds per square inch. Thermoplastic modified cyanate prepregs may belaminated at ambient pressures, or the preferred method is to use vacuumlamination. With vacuum lamination method, the environment in thevicinity of the prepreg/copper stack is evacuated to a pressure of -29.5inches Hg using either a vacuum frame around the stack, or by enclosingthe platens in a vacuum enclosure. The vacuum method is the preferredembodiment for making well consolidated, void-free laminates.

An alternate method for fabricating copper clad cores is to use acontinuous lamination process. There are two embodiments of this method;the first involves continuously laminating prepreg manufacture usingstandard impregnation towers between two sheets of a continuously movingroll of oxide treated copper foil. Heat and pressure are applied by ahighly polished stainless steel belt on both sides of the laminate.Typical double belt laminators are available from either Simplekamp orHeld Corporations. The preferred embodiment involves the production ofcopper clad cores using a melt impregnation of the moving web. Thiseliminates the need for producing prepreg on a large impregation tower.In this embodiment, the resin is melted and applied to a roll ofreinforcement (E-glass, K-glass, D-glass, S-glass, Technora paper,Thermount paper) by a doctor blade or slit die extrusion head. A thinfilm of molten resin is applied to a continuously moving oxide treatedcopper foil and is placed in contact with the moving web of thereinforcement. Molten resin may be applied to the top surface of themoving reinforcement or applied to a second roll of oxide treated copperfoil. Prior to entering the double belt portion, the two copper foilsand the reinforcement materials are brought into contact. The moltenresin is forced into the reinforcement in the consolidation zone of thedouble belt laminator with the further application of highertemperatures and pressure. The second method produces copper clad coresof high quality in a continuous fashion without having to handle largevolumes of volatile solvents.

Another application utilizes the TPM cyanates impregnated into anexpanded polytetrafluoroethylene (ePTFE) reinforcement. Due to theproblems drilling woven expanded PTFE fibers, a new expanded PTFE matwas developed. Using a satisfactory process, a thermosetting resin isimpregnated into the mat. In fact, a commercial product based onnon-fluorinated bisphenol A dicyanate impregnated into an ePTFE mat isnow available. The mat is available in a wide range of thicknesses. Theadvantage of using the TPM cyanates, over the commercial product, isthat the fracture toughness of the matrix resin is substantiallyenhanced compared to the standard polycyanurate material. Furthermore,the dielectric constant of the TPM cyanates is lower compared with thenon-fluorinated polycyanurates. The combination of the low dielectricconstant of the toughened polycyanurates coupled with the extremely lowdielectric constant of PTFE yields a dielectric layer with a dielectricconstant in the range of 2.3-2.5 depending on the resin content. Thisprovides a means to use a more conventional lamination approach (i.e.thermosetting polymer laminated in a flat-bed press).

Another embodiment of the present invention is the use of thecomposition thereof in electronic circuit packages. The generalstructures and manufacturing processes for electronic packages aredescribed in for example, Donald P. Seraphim, Ronald Lasky, and Che-YoLi, Principles of Electronic Packaging, McGraw-Hill Book Company, NewYork, N.Y., (1988), and Rao R. Tummala and Eugene J. Rymaszewski,Microelectronic Packaging Handbook. Van Nostrand Reinhold, New York,N.Y. (1988), both of which are hereby incorporated herein by reference.

The basic process for polymer based composite package fabrication isdescribed by George P. Schmitt, Bernd K. Appelt and Jeffrey T. Gotro,"Polymers and Polymer Based Composites for Electronic Applications" inSeraphim, Lasky, and Li, Principles of Electronic Packaging, pages334-371, previously incorporated herein by reference, and by Donald P.Seraphim, Donald E. Barr, William T. Chen, George P. Schmitt, and Rao R.Tummala, "Printed Circuit Board Packaging" in Tummla and Rymaszewski,Microelectronics Handbook, pages 853-922, also previously incorporatedherein by reference.

Articles can be used in electronic circuit packages prepared having aplurality of layers wherein at least one of the layers is formed of acurable material comprising a fluorine containing cyanate and a fluorinecontaining thermoplastic polymer material which is cured. One or more ofthe remaining layers is formed of a thermoplastic or thermosettingresin, the particular resin to be selected based upon the desiredproperties to be utilized. To function efficiently as an electroniccircuit package, the article described above contains electricallyconductive metal patterns embedded therein which serve as a carrier foran electric circuit. Further discussion of electronic circuit packagesis found in U.S. Pat. No. 5,103,293 to Bonafino et al., the contents ofwhich are hereby incorporated by reference herein.

The articles formed are generally multilayer articles of two up tothirteen or fourteen layers comprising an electrically conductivecircuit layer on a polymer, ceramic or multilayer substrate wherein thepolycyanurate thermoset material of the present invention is appliedover the electrically conductive circuit layer from a solvent solutionor from a melt solution to provide a dielectric layer having aplanarized outer surface after curing said thermoset material, saidarticle being characterized in having one set or a plurality ofalternating wiring networks in said thermoset material.

The other thermoplastic or thermosetting layers comprising the articlecan be the same or different and are selected from the group consistingof polyimide, photosensitive polyimide, epoxy, benzocyclobutene andpolycyanurate formed from photosensitive cyanate resin.

EXAMPLE 1 Thermoplastic Modifier Synthesis--Bisphenol AF Polysulfone

To a 5 liter 4 neck round bottom flask equipped with a nitrogen inlet,thermometer, stirrer, and Dean Stark trap fitted with a condenser werecharged 437.11 gm 2,2'-bis(4-hydroxyphenol)hexafluoropropane, 319.34 gmdifluordiphenylsulfone, 225 gm potassium carbonate, 1775 mlN-methyl-2-pyrrolidinone and 775 ml toluene. The stoichiometry of thereactants was varied according to the Carrothers equation to achievehydroxyl-terminated oligomers of controlled molecular weight. Thereaction contents were placed under nitrogen and heated until thetoluene began to reflux at approximately 140°-155° C. The reactionmixtures was refluxed until complete dehydration was achieved(approximately 4 hours). The water released during phenoxide formationwas collected and removed from the Dean Stark trap. Toluene was drawnfrom the Dean Stark trap until the reaction temperature reached165°-170° C. The system was allowed to react for 10-12 hours, resultingin a viscous dark green solution. After cooling to approximately 80° C.,the reaction mixture was filtered to remove the inorganic salts. Thereaction solution was then acidified to a pH of less than 7 with glacialacetic acid and precipitated into a 10 fold volume of methanol and waterin a ratio of 25/75 (vol/vol), respectively. The precipitated oligomer(light tan powder) obtained by filtration was washed with methanol andwas then dried under vacuum at 100°-120° C. After drying the oligomerwas redissolved in tetrahydrofuran (30% solids concentration) and theprecipitation, filtration and washing procedures were repeated. Finally,the precipitate was dried at 120° C. to constant weight yieldingapproximately 700 gm of an oligomer possessing a molecular weight (<Mn>)of approximately 17,900 by size exclusion chromatography (GPC) andapproximately 17,600 using a titration method with tetramethylammoniumhydroxide in methanol. The oligomer possessed a glass transitiontemperature of 195° C. and a degradation temperature of approximately525° C. as measured by thermogravimetric analysis under nitrogen. Thedielectric constant of the oligmer measured at 1 kHz was approximately2.95.

EXAMPLE 2 Thermoplastic Modifier Synthesis--Bisphenol AF Polyetherketone

Using the same procedure described in Example 1, a bisphenol AFpolysulfone oligomer was synthesized by charging 33,6236 gm2,2'-bis(4-hydroxyphenol) hexafluoropropane, 21,0843 gmdifluorobenzophenone, 17.3 gm potassium carbonate, 130 mlN-methyl-2-pyrrolidinone and 45 ml toluene into a 500 ml flask. Theresulting oligomer possessed a glass transition temperature of 165° C.and a degradation temperature of approximately 550° C. as measured bythermogravimetric analysis under nitrogen. The dielectric constant ofthe oligomer measured at 1 kHz was approximately 2.85.

EXAMPLE 3 Preparation of Toughened High Tg Polycyanurate ThermosetMaterials

To a 100 ml two neck round bottom flask equipped with a gas inlet andmechanical stirrer was charged 31.5 gm4,4'-(hexafluoroisopropylidene)diphenylcyanate (AroCyF-10 resin fromRhone-Poulenc) and 13.5 gm bisphenol AF polysulfone (30 wt/wt percent).The mixture was heated to 120° C. with stirring. After melting of thecrystalline solid occurred at approximately 90° C., the reaction wasplaced under vacuum for degassing and dissolution of the bisphenol AFpolysulfone in the dicyanate resin. In approximately 0.5-1.5 hours, themixture became homogenous and ceased bubbling, indicating that all ofthe moisture and dissolved gasses were removed. At this point, thetransparent, homogenous solution was poured into a preheated RTVsilicone rubber mold containing shapes appropriate for mechanicalproperty evaluation. Once filled, the mold was covered with a sheet of0.01 mil Teflon and was weighted down with a 0.25 inch thick piece ofaluminum. The mold was then placed into a forced-air convention oven andwas cured under nitrogen at 200° C. for 2 hours and at 310° C. for anadditional hour. The resulting samples were transparent and appeared tobe completely homogeneous; however, dynamic mechanical analysis (DMTA)demonstrated two glass transition temperatures (Tg) at approximately199° C. and 315° C. indicating phase separation. Attempts tocharacterize the phase separation with scanning electron microscopy(SEM) and transmission electron microscopy (TEM) were unsuccessfulsuggesting a very high degree of compatibility and submicron phaseseparation. The toughened thermoset samples exhibited fracture toughnessvalues of Klc=1.03 MPa √m and Glc=340 J/m2 from plain stain fracturetoughness tests. The dielectric constant of the toughened thermoset at 1kHz was approximately 2.7-2.8.

EXAMPLE 4 Preparation of a Reduced Cure Temperature ProcessableToughened Polycyanurate

A low Tg toughened polycyanurate network was prepared by blending anon-fluorinated dicyanate, specifically4,4'-(1,3-phenylenediisopropylidene) diphenylcyanate (M-dicyanate), with4,4'-(hexafluoroisopropylidene) diphenylcyanate (6F-dicyanate) in a60/40 (wt/wt percent) ratio, respectively. Bisphenol AF polysulfone wasalso added in 15 wt/wt percent (based on cyanate monomer weight) fortoughness enhancement.

For the sake of simplicity in describing the respective amounts of theconstituents of the multi component blends used in the presentinvention, the percentages are set forth according to the sequenceA(NF_(c) /F_(c))/B wherein A represents the total cyanate/polycyanuratecomposition in percent by weight of the blend; the symbols NF_(c) /F_(c)represents the non-fluorinated cyanate/polycyanurate to fluorinatedcyanate/polycyanurate in the total cyanate/polycyanurate compositionwith the non-fluorinated compound always listed first; and B representsthe thermoplastic modifier expressed in percent by weight.

The mixture containing 11.9 gm of 6F-dicyanate, 17.85 gm of M-dicyanateand 5.25 gm of bisphenol AF polysulfone was prepared as described inExample 4.

A series of samples or varying blend compositions having various amountsof non-fluorinated and fluorinated polycyanurates and thermoplasticmodifiers were prepared as described in Examples 3 and 4 herein. Theresultant blends were formed into specific bars and tested for DMTA,fracture toughness and thermal analysis evaluation.

The dynamic mechanical behavior of modified polycyanurates materialsprepared as described in this Example 4 is shown in FIG. 3 for a 85(60/40)/15 composition. The tan δ trace demonstrates two transitions at199° C. and 234° C. for the polysulfone and polycyanurate phases,respectively, indicating presence of phase separation. However, thesamples were transparent and homogeneous, thus suggesting the phaseseparation is on the angstrom to nanometer scale.

Samples as detailed below were formed from blends having varying amountsof thermoplastic modifier contained therein according to the legendA(60/40)/B. These samples were formed into test specimen bars and testedfor fracture toughness. More specifically, FIG. 4 demonstrates theeffect of the thermoplastic modifier concentration on the fracturetoughness of modified polycyanurate thermosets containing 60%M-dicyanate and 40% 6F-dicyanate (wt/wt/) utilizing bisphenol AFpolysulfone as a modifier. From FIG. 4, it can observed that asubstantial increase in the fracture toughness is achieved withincreasing modifier concentration (B). Indeed, the toughness increasesfrom 250 J/m² to >650 J/m² with 30% (wt/wt) incorporation of thethermoplastic modifier. Epoxy resins, on the other hand, only exhibitfracture toughness between 40-90 J/m².

Samples as detailed below were formed from blends having varying amountsof non-fluorinated and fluorinated material at a constant concentrationof thermoplastic modifier of 15%, i.e. [85(NF_(c) /F_(c))15]. Thesesamples were formed into test specimen bars and tested for fracturetoughness and thermal analysis, more specifically the glass transitiontemperature.

FIG. 5 demonstrates the effect of varying the cyanate blend composition(M-dicyanate and 6F-dicyanate) at a constant thermoplastic (bisphenol AFpolysulfone) modifier level of 15% (wt. PSF/wt. cyanate resin). As thepercentage of M-dicyanate is increased over the 6F-dicyanate component,the fracture toughness is relatively unaffected at low 5 percentages(<20%) of M-dicyanate. However, as the percentage of M-dicyanate isincreased (>20%) at a constant thermoplastic modifier contents of 15%(wt. modifier/wt/cyanate resin) the fracture toughness rises rapidlyfrom 190 J/m² to >400 J/m².

FIG. 6 illustrates the effect of cyanate resin blends on the thermoset(i.e. polycyanurate phase) Tg for blends of M-dicyanate in admixturewith 6F-dicyanate mentioned above. FIG. 6 depicts that the ultimate Tgof the cured thermoset can be tailored with the blend composition.Furthermore, it demonstrates that the M-dicyanate and 6F-dicyanate aremiscible (i.e., behave as a single component with no phase separation).

Two sets of samples were prepared having varying types and amounts ofpolycyanurates and various amounts of thermoplastic modifierconcentration [A(0/100)B and A(60/40)B]. FIG. 7 depicts the effect ofthe cyanate blend composition as a function of the thermoplasticmodifier (bisphenol AF polysulfone) concentration. The curve labeled"6F" contains 100% of the 6F-dicyanate with varying percentages of themodifier. The curve labelled "blends" contains a 60/40 (wt/wt) blend ofM-dicyanate and 6F-dicyanate, respectively, at various modifierconcentrations. The blends, containing the more flexible M-dicyanate,exhibit a higher fracture toughness at all concentration levels.

EXAMPLE 5 Preparation of 106 E-Glass Prepreg/Laminates/Circuit Boards

A resin solution was prepared in a 2 liter beaker by mixing a 60/40(wt/wt) blend of M-dicyanate prepolymer solution (598.4 gms of a 75%solution in MEK) with 6F-dicyanate prepolymer solution (398.9 gm of a75% solution in MEK) and 470.7 gm of MEK. After thorough mixing, 132 gmof bisphenol AF polysulfone (15 wt/wt percent) was added (portionwise)and was stirred mechanically until complete dissolution was achieved.The resulting varnish was crystal clear, amber colored liquid,indicating complete dissolution of all components in the methyl ethylketone. Approximately, one hour prior to use, the above mentioned resinsolution was catalyzed with 200 ppm of manganese octanoate (25.0 gm of a0.006% solution in MEK). The resin solution was impregnated into a 106style, E-glass and K-glass reinforcing fabric using an impregnationtreater tower. The resulting prepreg was heat treated at 140° C. forapproximately 4 minutes to remove the MEK solvent and to "B-stage" theresin.

The prepreg was cut and laminated into test specimens which were usedfor determining the dielectric constant moisture absorption, coefficientof thermal expansion copper peel strength and interlaminate bondstrength. The results of these evaluations are summarized in Tables 1-3.

Copper clad laminates, upon which the copper peel test was conducted,and circuit boards were prepared by superimposing several layers of theprepreg between one or more sheets of copper. These structures werecured at approximately 250° C. to 325° C. under approximately 300 psi ofpressure for approximately two hours.

Parallel plate dielectric constant tests were conducted on the samples.The results are set forth in Table 1. Thermal analysis tests were alsoconducted on samples to determine the glass transition temperature.

                                      TABLE 1                                     __________________________________________________________________________    COMPOSITION           DIELECTRIC                                                                            IN-PLANE CTE                                    OF MODIFIED                                                                              GLASS      CONSTANT                                                                              (PPM/°C.)                                POLYCYANURATE                                                                            REINFORCEMENT                                                                            (AT 1 GH.sub.Z)                                                                       BELOW T.sub.g                                                                        ABOVE T.sub.g                            __________________________________________________________________________    95(60/40)/5                                                                              E-glass    3.5     --     --                                       90(60/40)/10                                                                             E-glass    3.4     --     --                                       85(60/40)/15                                                                             E-glass    3.4     16     8                                        80(60/40)/20                                                                             E-glass    3.4     --     --                                       95(20/80)/15                                                                             E-glass    3.4     --     --                                       85(80/20)/15                                                                             E-glass    3.5     --     --                                       85(40/60)/15                                                                             K-glass    3.2     --     --                                       85(60/40)/15                                                                             K-glass    3.2     13     6                                        __________________________________________________________________________

Table 1 demonstrates that the dielectric constant was essentiallyunaffected by the addition of the thermoplastic modifier and byvariation of the polycyanurate blend composition. However, it can beobserved that a significant decrease in the dielectric constant wasachieved by replacing the E-glass reinforcement with K-glass.

                  TABLE 2                                                         ______________________________________                                                        MOISTURE ABSORPTION                                                           (percent weight gain)                                         COMPOSITION       24 hour soak                                                                             16 hours                                         (ALL E-GLASS LAMINATES)                                                                         (room temp.)                                                                             (boiling water)                                  ______________________________________                                        FR-4 Epoxy Resin  0.30       2.57                                             95(60/40)/5       0.30       0.55                                             90(60/40)/10      0.28       0.52                                             85(60/40)/15      0.28       0.53                                             80(60/40)/20      0.31       0.58                                             85(0/100)/15      0.57       1.01                                             85(20/80)/15      0.27       0.56                                             85(40/60)/15      0.10       0.42                                             85(60/40)/15      0.28       0.53                                             85(80/20)/15      0.50       0.83                                             ______________________________________                                    

Table 2 shows a comparison of the moisture absorption for a typicalepoxy resin and several thermoplastic modified polycyanuratecompositions. The results demonstrate at the absorption is significantlyless for the modified polycyanurate compositions especially for thesamples boiled in water for 16 hours.

                  TABLE 3                                                         ______________________________________                                                          Copper Peel*                                                                             Interlaminate                                    COMPOSITION       Strength   Strength                                         (ALL E-GLASS LAMINATES)                                                                         (lbs/in.)  (lbs./in.)                                       ______________________________________                                        95(60/40)/5       7.4        8.8                                              90(60/40)/10      8.4        10.0                                             85(60/40)/15      8.5**      10.2                                             80(60/40)/20      8.4        11.3                                             85(0/100)/15      9.4        8.6                                              85(0/100)/15      9.8        8.4                                              85(20/80)/15      9.3        9.0                                              85(40/60)/15      8.5        10.2                                             85(60/40)/15      4.8        4.0                                              85(80/20)/15      0.50       0.83                                             ______________________________________                                         *All with 1 oz Gould copper foil, 90° peel test.                       **85(60/40)/15 with enhanced surface treatment copper foil produced a         value of 10.5 lbs/in., 90° peel test.                             

Table 3 demonstrates the results achieved for the copper peel andinterlaminate bond strengths. Furthermore, interlaminate bond strengthwas directly proportional to the fracture toughness increases depictedin FIG. 3.

The values obtained for the copper peel strength are comparable to FR4epoxy resin. The interlaminate bond strengths for the thermoplasticmodified polycyanurates far exceed those of epoxy resins.

EXAMPLE 6

Preparation of co-poly-p-phenylene 3,4'oxydiphenylene terephthalamide(PPODTA) Paper (aramid fiber mat) Prepreg/Laminates. PPODTA paper wasdried in a forced air oven for 1 hour at 110° C. to remove any residualmoisture in the aramid fiber mat. Failure to dry the aramid fiber matprior to impregnation results in blistering during the lamination of thecomposite. The resin solution described in Example 5 above was utilized,however, in order to get good penetration of the resin solution, thesolids content in the varnish was reduced to 45 percent. Thissignificantly lowered the viscosity and permitted good wetting of thearamid fibers.

The resin solution was then impregnated into the aramid fiber mat usingan impregnation treater tower. The resulting prepreg was heat treated at140° C. for approximately 4 minutes to remove the MEK solvent and to"B-stage" the resin. Laminates were then fabricated by superimposingseveral layers of the prepreg and curing them at approximately 250° C.under approximately 300 psi of pressure for two hours. Test specimenbars were prepared and tested to determine dielectric constant andin-plane coefficient of thermal expansion.

The resulting laminates possessed a dielectric constant of 2.8 (asmeasured at 1 GH_(z)). The in-plane coefficient of thermal expansion was14 ppm/°C. below T_(g) and -7 ppm/°C. above T_(g).

EXAMPLE 7 Thermally Conductive Toughened Polycyanurates

Solution cast films of thermally conductive polycyanurates were preparedby adding 60 gm aluminum nitride (portionwise) to 85 gm of cyanateprepolymer in MEK (75% solids concentration). The cyanate prepolymerswere in a ratio of 40/60 wt/wt percent M-dicyanate/6F-dicyanate.Propylene glycol monomethylether acetate (PGMEA) was added as a "tailsolvent" such that the overall ratio of MEK to PGMEA was 4:1respectively. The mixture was milled in a vessel containing steel shotsas media. Following milling, 6.0 gm bisphenol AF polysulfone (50% solidsconcentration in MEK) and approximately 100 ppm catalyst were added withstirring. The mixture was then coated on a substrate, dried under vacuum(for solvent removal) and cured at 180° C. for 2 hours and at 220° C.for an additional hour to form heat conductive dielectric composites.The above procedure can be applied to other heat conductive pigmentslike aluminum oxide and boron nitride.

What we claim and desired to protect by Letters Patent is:
 1. Anelectronic circuit package comprising an electrically conductive circuitlayer on a polymer, ceramic or multi-layer substrate wherein a curabledielectric material is applied over the electrically conductive circuitlayer, said curable dielectric material comprising a blend of afluorine-containing cyanate and a fluorine-containing arylene etherpolymer wherein said cyanate is a monomer having the structure

    N.tbd.C--O--R--[R.sup.1 ].sub.n --O--C.tbd.N

said fluorine containing arylene ether polymer has the structure

    X--R--[R.sup.1 ].sub.m --X

wherein X is any group capable of reacting with a --C.tbd.N group; R isan aliphatic or aromatic group which may or may not befluorosubstituted; R¹ is an aliphatic or aromatic group which may or maynot be fluoro substituted or R¹ is selected from the group consisting ofether, carbonyl, sulfone, phosphine oxide and sulfide, and at least oneof R or R¹ must be fluoro substituted; n is 0-10; and m is 0-100; saiddielectric material in the cured state comprising a fluorine-containingpolycyanurate network having a plurality of discrete phases of saidfluorine-containing thermoplastic polymer dispersed therein wherein saidthermoplastic polymer phases are of submicron size.
 2. The electroniccircuit package of claim 1 wherein said curable dielectric materialfurther comprises a nonfluorine-containing cyanate having the structure

    N.tbd.C--O--R.sup.2 --[R.sup.3 ].sub.n --O--C.tbd.N

wherein R² is an aliphatic or aromatic group; R³ is an aliphatic oraromatic group or R³ is selected from the group consisting of ether,carbonyl, sulfone, phosphine oxide and sulfide; and n is 0-10.
 3. Theelectronic circuit package of claim 1 wherein said curable materialfurther comprises a thermosetting monomer or prepolymer selected fromthe group consisting of epoxy, bismaleimide, benzocyclobutene,bisnadimide and diacetylene resins.
 4. The electronic circuit package ofclaim 1 wherein the curable dielectric layer is applied over theelectrically conductive circuit layer from a solvent or melt solution.5. The electronic circuit package of claim 1 wherein the electricallyconductive circuit layer comprises one or more sets of alternatingwiring networks.